Seat back



FIG. 1 is a first rear perspective view of my design;

FIG. 2 is a front perspective view;

FIG. 3 is a second rear perspective view;

FIG. 4 is a right side view;

FIG. 5 is a left side view; and,

FIG. 6 is a top perspective view of my design.

The broken lines showing portions of a seat back are included for the purpose of illustrating unclaimed subject matter and form no part of the claimed design. 

CLAIM The ornamental design for a seat back, as shown and described. 